A rapid scanning microspectrophotometer has been designed and constructed which allows absorption spectra to be measured between 350 and 650 nm at a speed of 0.6 msec per wavelength band (10 nm). Experiments on frog (Rana pipens) are in progress to measure the effects of several variables on visual pigment (rhodopsin) kinetic changes. These variables include pH, temperature, divalent cations, presence and absence of pigment epithelium and degree of attachment of rod outer segments.